The fact that vitamin D plays a role in the relationship between exercise and risk of heart disease is a new finding," says the study's lead author Andrea Chomistek, a researcher at the Harvard School of Public Health. "This likely comes from being outside more. People who exercise tend to be out in the sun, which raises their vitamin D level. I don't think you'd get the same increase in vitamin D by staying inside and running on the treadmill."
Chomistek and colleagues analyzed the activity levels and the blood work of men in the Health Professionals Follow-Up Study. During 10 years of follow-up, 412 men had a heart attack and were matched to a control group of 827 men who did not have heart disease.
The findings reported in October's Medicine & Science in Sports & Exercise, the journal of American College of Sports Medicine:
•Vigorous exercise was associated with higher levels of HDL (good) cholesterol, which accounted for 38% of the decreased risk of heart disease.
•Those who exercised also had higher levels of vitamin D and lower levels of hemoglobin A1c (a marker of diabetes risk), apolipoprotein B (a blood protein) than those who were inactive.
Other studies show that those who do regular moderate physical activity, such as brisk walking, have a 20% lower risk of heart disease, she says. "Moderate and vigorous exercise may have similar benefits for reducing your risk of heart disease as long as you burn a similar amount of energy," Chomistek says.